The present invention relates to integrated circuit fabrication processes, and specifically to post-etch cleanup procedures.
In integrated circuit fabrication, a wide variety of chemistries are used for etching thin layers. Among the most versatile (and strongest) chemistries are fluorine-based chemistries. Such chemistries are used for oxide etching, for tungsten etching, and (in combination with an oxygen source) for photoresist removal (commonly referred to as "ashing"). However, fluorine-based chemistries tend to leave some fluorine contamination.
The present inventors have discovered that residual fluorine contamination in metal layers is a cause of reduced adhesion, higher contact resistance, and diminished nucleation of subsequently deposited layers. Specifically, the adhesion and electrical contact problems of aluminum which has been exposed to an ashing process are due to formation of metal fluorides and/or oxyfluorides. Furthermore, aluminum in thin films forms a thin but durable native oxide (which is primarily Al.sub.2 O.sub.3) on exposure to air, so that the material self-passivates; but the presence of fluorine contaminants produces a lower density passivation layer, so the self-passivation is not as good. Thus, residual fluorine contamination is a serious problem.